In recent years, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a battery module having a plurality of battery cells electrically connected to each other because high output and large capacity are necessary for the middle or large-sized devices.
Preferably, the battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (a unit cell) of the battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing cost of the pouch-shaped battery is low, and it is easy to modify the shape of the pouch-shaped battery.
Battery cells constituting such a battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-output, large-capacity secondary batteries during the charge and discharge of the secondary batteries. In particular, the laminate sheet of each pouch-shaped battery widely used in the battery module has a polymer material exhibiting low thermal conductivity coated on the surface thereof with the result that it is difficult to effectively lower the overall temperature of the battery cells.
If the heat, generated from the battery module during the charge and discharge of the battery module, is not effectively removed from the battery module, the heat accumulates in the battery module with the result that deterioration of the battery module is accelerated. According to circumstances, the battery module may catch fire or explode. For this reason, a high-output, large-capacity battery module needs a cooling system for cooling battery cells mounted in the battery module.
The cooling system is generally configured to forcibly circulate a coolant in a battery module in order to remove heat from battery cells constituting the battery module. That is, the cooling system is configured to cool battery cells or unit modules constituting the battery module through contact between a coolant and the surfaces of the battery cells or the unit modules. Gas, such as air, is used as the coolant. Consequently, the cooling system may be a contact-based air cooling type cooling system.
However, it is necessary for the cooling system of the battery module to be configured such that the coolant uniformly reaches to the respective battery cells constituting the battery module. In a case in which the battery module is manufactured using a plurality of members capable of improving cooling efficiency, therefore, the size of the battery module as well as manufacturing cost of the battery module is increased. In addition, it is difficult to install a battery system, such as a battery module, having a large size in a limited space, such as an electric vehicle (EV) or a hybrid electric vehicle (HEV). For this reason, there is a high necessity for a cooling system that is capable of exhibiting high cooling efficiency while being configured to have a compact structure.
In addition, a short circuit occurs in a battery cell due to exposure of the battery cell to a high-temperature environment or malfunction of the battery cell, an electrolyte is decomposed on a positive electrode interface of the battery cell with the result that a large amount of gas is generated, whereby the internal pressure of the battery cell is increased. According to circumstances, a battery case may be ruptured, and the gas may be discharged out of the battery cell. In general, the internal gas of the battery cell contains a toxic component, such as carbon monoxide, which is harmful to humans. In a case in which the gas discharged from the battery cell and the coolant flowing in the battery module is mixed with each other, cooling efficiency is reduced, and at the same time, the safety of the battery module is reduced. For example, in a case in which the battery module is mounted in a vehicle, the gas generated in the battery cell may be introduced into driver and passenger spaces of the vehicle during the circulation of the coolant with the result that humans suffer harmful health effects.
Consequently, there is a high necessity for a battery module configured to have a structure that is capable of preventing mixing of gas generated in a unit cell and coolant flowing along a coolant flow channel while having a compact structure and exhibiting excellent cooling efficiency.